>>> type(sys.stdin)
<class 'idlelib.rpc.RPCProxy'>
Don't attempt sys.stdin._RPCProxy_methods lest you be turned to
stone ;-)
We didn't implement all the features of stdin as it didn't seem
necessary. Did you have a specific reason to access
stdin.fileno() ?
stdin/out/err support communications between the subprocess and
the IDLE GUI through a socket. They are redirected in the GUI and
proxied in the subprocess.